Marine mammals as a group are protected by the Marine Mammal Protection Act because their numbers have been severely reduced through hunting and habitat destruction. It is believed that large whales which emit low frequency sound for sensing and communication and other marine mammals which dive into the deep sound conduction channel are most vulnerable to exposure to manmade sources emitting low frequency sound. Currently, an adequate understanding of the effects of manmade sound on the environment does not exist. Yet, an understanding of the effects of low frequency sound on animals in the marine environment is necessary to create new legislation and management practices to protect the environment.
This project develops state of the art monitoring and mitigation capabilities for assessing the impacts of manmade low frequency sound on the marine environment.
Sound levels around a sound source are measured to calibrate the effectiveness of planning models of transmission loss. The acoustic monitors can be bottom mounted, moored, drifting, or attached to a mobile platform (i.e., ship or animal). Both visual and acoustic monitoring are used to assess the abundance and distribution of marine mammals around the sound source. Using a variety of methods, the behavioral and physiological responses demonstrated are measured before, during, and after a test sound is produced. Remote sensors are attached to the animals to monitor heart rate and vocal activity and to determine the sound level actually received by the animal. The change in swim speed or direction and the alteration of normal swim patterns is measured as well. Long-term effects of exposure to low-frequency sound are measured using photographs of individual whales that then can be identified for further study at a later date.
Ten adult male elephant seals were tagged with acoustic dataloggers on their departure in March 1997. The sound source was not operating for the seals’ return in August, so these samples will be added to the control. Aerial surveys and photo identification were performed until the sound source failed in March. Data analysis of 1996 acoustic tag data showed no indication of behavior modification at received sound levels as high as 130 dB. Playback studies to sperm whales in the Azores and humpback whales off the Kohala coast exhibited no effects for received levels in excess of 140 dB. The Bodega Marine Lab found no effects on boney fish for received soundlevels as high as 145 dB.
The data collected will enable the development of new technology to improve the detection and monitoring of marine mammals. The results derived from this technology will be implemented in new laws governing not only Naval actions, but commercial and recreational activities that emit low frequency sound as well.